Battery Parasitic Draw Diagnosis

[toolman.dustin]

Diagnosing what's draining your battery can be very frustrating. I put together this email after helping my daughter find the source of battery drain in her 2003 Highlander. I suspect this will be helpful to many followers of this forum.
This won't likely help diagnose what's draining your trailer battery since we all lean very quickly, there's a lot of stuff connected to your trailer battery that doesn't run through your circuit breakers or fuses. If you're willing to spend the time, you will learn quite a bit on how to diagnose electrical problems with much less "mystery".


Battery Parasitic Draw Diagnosis
How to diagnose why your battery keeps going dead:

Though lengthy, all three videos are worth watching. You'll
learn a lot about how to diagnose car electrical problems.

The long video has a lot of talking but every once in a while he says something you don't want
to miss.

New cars anything over .2 amps is parasitic draw, because of computers.

Older cars anything over .05 amps will be parasitic.

Battery Parasitic Draw (short video) 4:47
How to connect the multimeter
Pull fuses to isolate. - on new cars this can cause the computer to
wake up and you may have to wait 30 minutes for it to go back to sleep.
Pull relays to isolate - on new cars this can cause the computer to
wake up and you may have to wait 30 minutes for it to go back to sleep.

Long video 33:00

very long video but worth watching:
5:43 - charge battery weak battery will cause lots of problems
connect clamp on amp meter
28:46 how to connect multimeter without clamp


/////
At 13:24 in this video the technician measures the voltage drop across a fuse and then
using a lookup table (below) determines the current flowing through that fuse. This is how
He determines which circuit is exhibiting parasitic draw on the battery.

Lookup Table - Amperage through a fuse by measuring the Voltage drop across a fuse:
better table - https://www.powerprobe.com/resource/20240904232955310.pdf


fuse types:
parasitic


Dustin

 

[Hoopy Frood]

I found the best tool for my usage, for my trailer, is a clamp-on amp meter. I can easily, okay not really easily, but not too badly, track down which wires are pulling the higher amps. I think it's a tool that belongs in a trailer electrical tool box.

 

[Butcher]

New cars anything over .2 amps is parasitic draw, because of computers.

No way!

If you had that kind of draw, I suspect your battery would be too low to start after a week. That is totally unacceptable for a new car owner and therefore no manufacturer would even think that is a good idea.

40 years in the business of fixing Mercedes/BMW's, 40mA [0.04A] is the max draw once the car is 'asleep'. This may take as much as an hour to get to that stage, but that is that is the max spec. Typically, I see 30mA or less.

Without a doubt, a mA amp clamp is the ONLY way to find a draw. Sometimes computers reset when the battery is disconnected and it's difficult to hook up an old school amp meter without some type of disconnection from the battery. The other issue is that many hand held meters have fuses that will blow if the current gets too high. So, if you are checking mA, the use may be as low as 400mA and the slightest consumer turning on will blow your fuse. It gets to be real frustrating when you are blowing fuses in your meters.

The voltage drop on fuses is the second best I have found when locating a draw. It can be a bit more difficult to probe the fuses.

 

[traveldawg]

No way!

If you had that kind of draw, I suspect your battery would be too low to start after a week. That is totally unacceptable for a new car owner and therefore no manufacturer would even think that is a good idea.

40 years in the business of fixing Mercedes/BMW's, 40mA [0.04A] is the max draw once the car is 'asleep'. This may take as much as an hour to get to that stage, but that is that is the max spec. Typically, I see 30mA or less.

Without a doubt, a mA amp clamp is the ONLY way to find a draw. Sometimes computers reset when the battery is disconnected and it's difficult to hook up an old school amp meter without some type of disconnection from the battery. The other issue is that many hand held meters have fuses that will blow if the current gets too high. So, if you are checking mA, the use may be as low as 400mA and the slightest consumer turning on will blow your fuse. It gets to be real frustrating when you are blowing fuses in your meters.

The voltage drop on fuses is the second best I have found when locating a draw. It can be a bit more difficult to probe the fuses.

I hate to be the bearer of bad news, but a lot of new cars and trucks will die after a week or maybe 10 days at the most because they are so heavily laden with electronics, onboard modems that both talk to the manufacture and the app on smartphones, etc.

I have to leave a trickle charger on my truck or it goes into "sleep mode" after about a week. And I have good batteries. I think "deep sleep" means, among other things, it stops using the onboard modem.

It's not a happy site when one goes on a two week vacation and leaves one's vehicle at a park and ride lot. 'Carry a battery' booster has become a good recommendation.

 

[Butcher]

Without a doubt, if the battery does not stay charged after two weeks, you got problems. It could be as simple as a weak/worn battery. There is no way I could convince anyone that is normal. Some of my clients were very wealthy geeks that would rip me up one side and down the other if I told it's normal for a battery to go dead that fast.

I've worked on German products my entire working life [still am]. My job for well over 20 years was to only work on cars that could not be fixed. Trust me when I say, I've probably got more time looking for draws than most mechanics. Dead batteries were something Mercedes customers were familiar with. Many of the millionaires/billionaires I've worked with had too many cars to drive at the same time. They consistently were concerned with dead batteries. My experience was that if the battery was dead in less than 45 days, there was a potential of an issue.

Google 'normal Parasitic draw on a new vehicle'. You might change your opinion. If not, maybe I can change others that read this. 0.2A is not normal for a modern gas/diesel powered vehicle, never was and never will be.

I'm not here to change your opinion, you do you and I will do me. I'm hear to share some facts so others can form their own opinion.